Well it's not like we're not trying to invent better batteries, but it's hard to do. Doubling capacity would already be huge, several orders of magnitude would make you a billionaire. I don't see it happening anytime soon. Furthermore, Lithium can be a strategic resources (e.g. half the world's supply is in bolivia) which could mean a significant bottleneck if we start using them on a large scale for a flexible energy network. A regular house roof is enough to be mostly neutral. Significant strides are made in the energy efficiency of a house. Better management of energy flows can result in city heating from industrial waste heat, reducing the energy requirements further.